Reciprocating engines such as internal combustion engines and compressors force small amounts of the gaseous media they compress past seal rings and into the crankcase. The gaseous media, which passes through the seal rings is normally referred to as blowby and collects in the crankcase partially filled with lubricating oil. The lubricating oil is highly agitated by the crankshaft and connecting rods forming small oil droplets and mist, which become entrained in the gases in the crankcase. The crankcase is normally hot causing some of the oil to vaporize. To avoid a build up of pressure in the crankcase, the blowby is exhausted from the crankcase to the atmosphere. In internal combustion engines the blowby can be returned to the engine intake or to the exhaust.
The presence of lubricating oil in the blowby from reciprocating machines is environmentally undesirable and difficult to remove, since it is normally in the form of droplets, submicron mist and vapor. In internal combustion engines lubricating oil in the blowby is also accompanied by environmentally harmful products of combustion. To mitigate the affect of the harmful elements in the blowby, the blowby is readmitted to the normal flow of air and fuel to the engine or to the hot exhaust gasses to provide more complete oxidation of the elements in the blowby. The blowby from reciprocating compressors can not be returned to the compressor inlet as the presence of lubricating oil in the compressed gases is normally undesirable.
Filters only remove particulate material, liquid droplets, liquid mist, and submicron sized droplets; but, allow oil vapor to pass through. Water vapor is also found in the typical blowby from reciprocating engines and normally in large quantities relative to oil vapor. If the water vapor condenses to liquid it will saturate the oil filter media and block the flow. The collected water may also freeze in cold weather.
U.S. Pat. No. 5,456,239 shows a crankcase ventilation system for an internal combustion engine having a supercharger and an after cooler in which the crankcase blowby is returned to the engine inlet manifold by an accumulator having a diaphragm pump operated by switching the pressure on one side of the diaphragm from the pressure at the inlet of the supercharger to the pressure at the exit of the supercharger to pump the crankcase blowby into the inlet manifold.